Mesa Repo Updated To 17.2.6

Andres Gomez has announced another bugfix release of Mesa last weekend. I haven't had any time to upload it – until now. Here's an overview:

In Mesa Core we have included a correction to keep a program alive when
re-linking and prevent an use-after-free.

The GLSL compiler has received several fixes, including one to prevent
a SIGSEV when calling an undeclared subroutine in certain conditions
and another to mark the xfb buffers as active only if a variable uses
them.

The SPIR-V compiler has corrected a couple of issues involving the
usage of separate images and texture/samplers.

The Intel drivers include many new fixes, specially for i965. Several
are focused on improving SIMD32 and little-core. It also includes a fix
for a GPU hang which was detected while playing HW accelerated video
with mpv.

The AMD drivers have also received some care. radv has seen plugged 2
memory leaks while r600 has gotten a fix through reversing the tess
factor components for isolines.

The swr driver has corrected two performance regressions, one for the
avx512 platforms and the other for the avx/avx2 platforms.

In the ddebug gallium driver we have a fix for an use-after-free.

On the EGL side, the Wayland platform of the the DRI2 drivers has
received a fix to prevent crashing in ancient systems.

GLX has also received corrections to prevent a couple of errors when
creating and binding a context in DRI3 and DRISW, respectively.

From build and integration point of view, we have added some few more
fixes, including one to allow building libglvnd when EGL is present but
not GLX, another to enable building targets which don't need X11, such
as omx and va, when XCB is not present, and another one to be able to
specify the prefix installation for the OpenCL icd file.